1. Technical Field
The present invention relates reciprocating internal combustion engines having individual cylinder fuel control and camshaft timing control.
2. Disclosure Information
In the interest of reducing fuel consumed by automotive engines, it is desirable to shut off fuel delivery when the engine is decelerating. This is termed deceleration fuel shut off (DFSO). A problem with such deceleration arises with respect to engines having exhaust aftertreatment systems, however. If fuel is shut off to an engine during deceleration, but the airflow through the engine continues unabated, the aftertreatment system will become loaded with oxygen and this will cause an excess amount of oxides of nitrogen (NOx) to be released once normal combustion is resumed. Unfortunately, even with the throttle in its closed or idle position, enough air will leak past and thereby cause the undesirable oxygen loading problem. And, although it is known to use port throttles and limited camshaft timing changes to control the gas flow through an engine during certain operating conditions, such a scheme will not work for the purpose of preventing the previously described NOx spike, because port throttling will allow some air to pass through the engine's cylinders, thereby loading the exhaust aftertreatment device with oxygen and causing the previously described increase in NOx when the engine is reactivated following a deceleration.
A system according to the present invention allows fuel to be shut off during engine deceleration without causing an increase in NOx during reactivation of the engine, because the engine's camshaft or valve timing is changed to the extent that regardless of the position of the engine's throttles, no net flow of mass, whether it be air, exhaust, or otherwise, will flow through the engine. In effect, charge is trapped in the engine and charge flow is halted.